The present invention relates to an exhalation valve used in a respiratory breathing circuit and which is utilized to control the exhalation of a patient utilizing that breathing circuit and to control the minimum pressure within that patient circuit.
There are presently various forms of exhalation valves for respiratory breathing circuits. One fairly popular commercial type is the mushroom valve wherein an inflatable bladder is located adjacent an opening through which the patient's exhaled breath passes. By inflating the bladder, that bladder expands to the point where it covers and thus seals the opening and prevents the passage of gas therethrough. One difficulty with such valve is, however, that it may materially deform after prolonged use and fail to provide an adequate seal.
A further type of exhalation valve, as shown in U.S. Pat. No. 4,241,756 includes a flexible diaphragm that covers the opening and a sealed chamber above the diaphragm is selectively pressurized to create a bias urging against the diaphragm to close the same or to retain a bias against that diaphragm urging it toward its closed position.
A difficulty with that flexible diaphragm type of valve is, however, that the flexibility of the diaphragm causes instability thereof, i.e. the diaphragm may not move uniformly from its seat but may flex only in a certain area thereof and thus release pressure in the patient circuit at a level unanticipated by the control pressure in the sealed chamber.
If, on the other hand, the diaphragm is comprised of a rigid material to overcome the flexing problem, the rigid diaphragm does not allow good sealing against the valve opening and leakage is a further difficulty.